The 5-sulfonyl substituted benzotriazole UV absorbers are useful for the stabilization of polymer systems against the harmful effects of UV and actinic light. These compounds and their compositions and applications are described more particularly in U.S. Pat. Nos. 5,280,124 and 5,436,349. Some sulfone-containing benzotriazoles are described in earlier patents by H-J. Heller et al., Swiss Patent No. 355,947, and U.S. Pat. Nos. 3,218,332 and 3,766,205. According to U.S. Pat. No. 3,766,205, a 5-thio derivative was synthesized from the corresponding sulfonic acid. The sulfonic acid was converted to its sulfonyl chloride which in turn is reduced to a thiol group and added to an acrylate ester to give the corresponding thiopropionate derivative.
The instant invention describes an improved process for the manufacture of 5-sulfonyl substituted benzotriazoles starting from the corresponding 5-chlorobenzotriazoles. This synthetic route has been mentioned by Kobayashi et al., Japanese Sho 62-288,630 and DesLauriers et al. in U.S. Pat. No. 5,319,091. In the Kobayashi case, the desired compounds are polymeric thioether derivatives of benzotriazoles and not the corresponding sulfonyl derivatives.
Kobayashi et al. describe a method of preparing polyarene thioethers in which benzotriazole moieties are covalently attached to the polymer via a thioether linkage. These transformations are carried out under aqueous, strongly alkaline conditions at temperatures of 200-290.degree. C. for a period of 20 minutes to 20 hours with preferably an organic amide present. The instant invention uses small non-polymeric thiol compounds at temperatures from 30-180.degree. C. in the presence of an alkali metal hydroxide in polar aprotic solvents. Additonally, Kobayashi et al. state "It is preferably from the viewpoint of stability of the polymer that the above-mentioned organic amide solution contain water in an amount of 2.5 to 25 parts by weight and that the obtained aqueous solution have strong alkaline properties. For example, in the case of the above-mentioned solvent is diluted with a tenfold quantity of water, it is recommended that the alkaline strength of the aqueous solution have a pH exceeding 9.5." See Japanese Sho 62-288,630, page 15.
In the present invention, additional water is not needed. In fact, the desired reaction can be done under anhydrous conditions giving high yields with excellent product quality. The above-mentioned addition of a tenfold quantity of water could complicate and hinder recovery and recycle of the polar aprotic solvent which is needed for economical and ecological reasons. Clearly, the instant process is outside the disclosure of Kobayashi et al.
DesLauriers et al. in U.S. Pat. No. 5,319,091 describe a process for preparing sulfur-containing derivatives of 2-(2-hydroxyphenyl)-2H-benzotriazoles. In their process, sulfur-containing aromatic compounds are reacted with chloro-substituted 2-(2-hydroxyphenyl)-2H-benzotriazoles to yield an aryl sulfide derivative. These aryl sulfide compounds are then contacted with oxidizing agents to give the corresponding aryl sulfone 2-(2-hydroxyphenyl)-2H-benzotriazoles. DesLauriers et al. describe a process for contacting sulfur-containing aromatic compounds with a halosubstituted 2-(2-hydroxyphenyl)-2H-benzotriazole. The instant process can employ sulfur-containing aryl or alkyl compounds giving a more versatile dimension to the present invention. A direct comparison of the instant and DesLauriers processes are given in Example 4 and illustrate the unexpected superior results obtained by the instant process.
DesLauriers et al. isolate the intermediate aryl sulfide and dry it before proceeding with the oxidation step. In the instant process, isolation of this intermediate is not required. In fact, a much improved yield is obtained when the intermediate is not isolated. In working Examples 2-3 of U.S. Pat. No. 5,319,091, the final yields the aryl sulfone 2-(2-hydroxyphenyl)-2H-benzotriazole compound relative to the starting benzotriazole 5-chloro reactant are 65% and 60.1%. The instant process gives a yield of 88.6% for the same product as seen in instant Example 1.
DesLauriers et al. report a step 1 yield of 72.6% for the isolation of the thioether intermediate in Example 1 of U.S. Pat. No. 5,319,091. The instant process yields the same thioether intermediate in a 97% yield, but isolation of this intermediate is not required in the instant process.
DesLauriers et al. oxidize the thioether derivative with either m-chloroperbenzoic acid (MCPBA) in methylene chloride or with hydrogen peroxide and tungstic acid (H.sub.2 WO.sub.4) in isopropanol. It is noted that, first, the use of MCPBA on an industrial scale has considerable disadvantages. These include the recovery and reuse of the waste m-chlorobenzoic acid which is a byproduct of this process. This recovery and reuse would be required to make this process economically and/or environmentally feasible. Second, using hydrogen peroxide, tungstic acid and isopropanol requires a reaction time of 12 hours. Even after 12 hours, 4.6% of 5-phenylsulfinyl-2-(2-hydroxy-3,5-di-tert-butyl-phenyl)-2H-benzotriazole and 0.8% of 5-phenylthio-2-(2-hydroxy-3,5-di-tert-butyl-phenyl)-2H-benzotriazole still remain.
On the other hand, the instant process using hydrogen peroxide, formic acid and sodium tungstate (Na.sub.2 WO.sub.4) in xylene requires only two hours or less of reaction time. High isolated yields (97%) and excellent product quality are obtained. Unexpectedly, when in the preferred oxidizing system the formic acid is replaced with acetic acid, only a 60% conversion to sulfoxide and virtually no sulfone product is obtained. Peracetic acid (hydrogen peroxide in acetic acid) is mentioned as a suitable oxidizing agent by DesLauriers et al. in U.S. Pat. No. 5,391,091.